Unfortunately, physical fitness is of little use against cancer.
I’m 59, healthy right now, work out in the gym for an hour every day, and could still very easily die in a few years.
It lifts your spirit, it gives you energy and hope (geez...not hopium again)...it tells your body and mind--right down to the cellular level--that you are willing to fight for your life.
At least if you exercise, you will die fighting. And that can't be a bad thing.